The liquid crystal on silicon (hereinafter, referred to as “LCOS”), a sort of reflective liquid crystal display, which forms a liquid crystal cell on a semiconductor substrate differently from a typical crystal liquid display, realizes a large screen in a high resolution having more than XGA grade in a small size in the order of 1 inch by arranging the elements of each pixel and a switching circuit in a high integration.
For such reasons, the LCOS panel has come into the spotlight as a display device of the projection system, and the technical development and commercialization of the LCOS panel and the projection display system using the same are actively in progress.
As methods to implement a full-color screen, the projection system has used a 3-panel method converting a white light into R (Red), G (Green) and B (Blue) lights, composing R, G and B lights implemented by three LCOS panels each corresponding to R, G and B lights as color images and projecting the images to a screen.
Such a general LCOS projection system comprises an illumination unit projecting the light, a composition unit composing each R, G and B image, imaged on the LCOS panel after the light is projected, as images, a projecting lens projecting the light composed in the composition unit, and a screen on which the light projected from the projecting lens is imaged. In particular, although the illumination unit, the composition unit and the projecting lens are commonly named as an optical engine, the optical engine is the part on which a high heat is generated by the illuminating light and if the high heat is not cooled, it causes the degradation of image quality.
Under such a background, a proper cooling system should be equipped so that the high heat is cooled. If the high heat is not cooled, it may cause problems that a plurality of films included in the illumination unit and the LCOS panels included in the composition unit are oxidized and further, the projection system is not normally operated.
However, during cooling by air injected for cooling operation, for the parts on which the image is formed, for example, the LCOS panel, it is important that the image is not deteriorated by foreign substance injected together with air. In detail, in case that the foreign substance are floated by a turbulent flow generated by the air injected for cooling or the foreign substance are injected together with air, it is apprehended that the foreign substance may contaminate a plurality of panels through which the light passes. Therefore, countermeasures thereof are required.